1. Field of the Invention
This invention relates to roadway paving materials and more particularly to an emulsion for adding rubber to asphalt paving material.
The benefits of adding rubber to asphalt paving were first proposed in the middle of the last century; however, it was not until about the middle of the present century that the idea of adding vehicle tire rubber to asphalt was developed and crumb rubber from vehicle tires was added. Crumb rubber in an asphalt emulsion proved to be elastic and flexible and is used as a crack sealer with satisfactory results.
It has been found that the use of crumb rubber from scrap vehicle tires added to asphalt also improves road durability. It is now a requirement that pavement asphalt contain a predetermined percentage of recycled rubber as the percentage of the total tons of asphalt laid which is financed in whole or in part by a Federal Assistance Program.
Most asphalts are products of the distillation of crude petroleum and range from hard and brittle-like solids to almost water-thin liquids. Asphalt cement is the basis of these products and may be liquefied for construction purposes by heating, adding solvents, or an emulsifier. Adding diesel fuel to base asphalt results in a product called "cut-back". The use of emulsions rather than cut-backs results in substantial fuel savings.
Asphalt dispersed in water with an emulsifier forms an emulsion.
The purpose of the emulsifier is dispersion of asphalt cement in water for pumping, prolonged storage and mixing. The emulsion should "break" quickly when it comes in contact with aggregate in a mixer or sprayed on a roadbed. When cured, the residual asphalt retains all the adhesive, durability, and water-resistant properties of the asphalt cement from which it was produced.
In the general method for emulsifying asphalt, concurrent streams of molten asphalt cement and water containing an emulsifying agent are directed by a positive displacement pump into a colloid mill and divided into tiny droplets by intense shear stress.
To accomplish its ultimate function of cementing and waterproofing, the asphalt must separate from the water phase. In "breaking" asphalt droplets coalesce and produce a continuous film of asphalt on the aggregate or pavement.
This invention provides a rubber containing emulsion easily added to substantially any conventional asphalt emulsion.
2. Description of the Prior Art
The most pertinent patents are believed to be U.S. Pat. No. 4,018,730 issued Apr. 19, 1977 to McDonald for METHOD FOR EMULSIFYING ASPHALT-RUBBER PAVING MATERIAL AND A STABLE THIXOTROPIC EMULSION OF SAID MATERIAL; and, U.S. Pat. No. 4,137,204 issued Jan. 30, 1979 to McDonald for CATIONIC METHOD FOR EMULSIFYING ASPHALT-RUBBER PAVING MATERIAL AND A STABLE THIXOTROPIC EMULSION OF SAID MATERIAL. U.S. Pat. No. 4,018,730 discloses a method requiring heat and an alkali hydroxide-asphalt emulsifier mixture, where the asphalt emulsifier is a resin, tall oil fatty acid, oleic acid, stearic acid, animal protein, or casein, for emulsifying an asphalt and reclaimed rubber pavement repair material into a thixotropic emulsion capable of flowing as a liquid upon agitation. U.S. Pat. No. 4,137,204 substantially discloses the same emulsion as a base and adds an asphalt-rubber soap containing a cationic water soluble emulsifying agent.
This invention is distinctive over these patents by forming an asphalt modifying emulsion, mixed under ambient temperature and containing a relatively high percentage of reclaimed rubber that may be added to and mixed with, under ambient temperature, substantially any known asphalt paving material mix containing less than a predetermined required percentage of rubber for increasing the rubber content thereof.